The formation and modulation of airway fluid is critically important for both lung development and postnatal lung function. Active C1- secretion by epithelial cells drives fetal lung fluid production. Although there are numerous modulators of C1- secretion, the Cystic Fibrosis Transmembrane Conductance Regulator, CFTR, is among the most important. In adult airway epithelial cells, CFTR mediates cAMP-dependent stimulation of C1-secretion. Its expression and function in fetal cells is unknown. the purpose of this grant is to investigate CFTR expression and function in a rabbit animal model of human lung development and thereby elucidate the role of CFTR function in lung development. CFTR expression and function during rabbit fetal lung development will be investigated using molecular and cell biological techniques. The work will be divided into two parts. The goal of Part I is to define the distribution of CFTR expression in fetal lung during development. Aim 1 is to measure CFTR mRNA expression in fetal rabbit lung and airways. Aim 2 is to determine the developmental sequence of CFTR protein expression in fetal rabbit lung and airways using immunological approaches. Aim 3 is to identify the cell type(s) in which CFTR is expressed in fetal lung by immunocytochemistry. Aim 4 is to compare the expression of CFTR in the lung with other fetal organs. The goal of Part II is to study the role of CFTR in fetal C1- and fluid secretion. Aim 5 is to study the regulation of C1- transport by fetal CFTR using electrophysiologic techniques. Aim 6 is to study the regulation of fluid secretion in lung bud explants by specific elimination of CFTR with antisense oligonucleotides.